Segment Information - Summary of Special Items (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
After-tax
Charge for organizational efficiency plan (Selling, general and administrative expenses)	$ 119	$ 119
Charge for organizational efficiency plan (Selling, general and administrative expenses)			$ 24	$ 162
Debt extinguishment costs		110	151	0
Integration and transaction-related (benefits) costs (Selling, general and administrative expenses)		71	404	427
(Benefits) charges associated with litigation matters (Selling, general and administrative expenses)		(21)	19	41
Risk corridors recovery (Selling, general and administrative expenses)		0	(76)	0
Contractual adjustment for a former client (Pharmacy revenues)		0	(155)	0
(Gain) on sale of business		0	(3,217)	0
Total impact from special items		279	(2,850)	630
Before-tax
Charge for organizational efficiency plan (Selling, general and administrative expenses)	$ 168	168
Charge for organizational efficiency plan (Selling, general and administrative expenses)			31	207
Debt extinguishment costs		141	199	0
Integration and transaction-related (benefits) costs		169	527	552
(Benefits) charges associated with litigation matters (Selling, general and administrative expenses)		(27)	25	51
Risk corridors recovery (Selling, general and administrative expenses)		0	(101)	0
Contractual adjustment for a former client (Pharmacy revenues)		0	(204)	0
(Gain) on sale of business		0	(4,203)	0
Total impact from special items		$ 451	$ (3,726)	$ 810